This invention concerns cationic core-shell particles having a polymeric core component and a polymeric shell component disposed generally about said core, wherein said shell contains a stabilizer that is covalently bonded to the polymeric shell component. More particularly, the invention concerns the use of these core-shell particles in formulating ink jet receptive coatings.
Ink jet printing is widely used to print on a variety of substrates (including paper, textiles, and plastic films). These substrates are often coated with a material that enhances their receptivity for the ink jet ink. Ink jet images are formed by spraying ink formulations, the majority of which are aqueous dye-based ink solutions, onto the ink jet receptive coating. The dyes are molecularly adsorbed on the surface of the coating, where they are subsequently exposed to ambient atmospheric pollutants and light. Over time, photochemical reactions and chemical reactions with oxygen, ozone, nitrogen oxides, and/or sulfur oxides commonly cause the dyes to fade.
A traditional method of attempting to improve the fade resistance of ink jet prints has been to add stabilizers to ink jet ink formulations. For example, U.S. Pat. No. 5,124,723 describes ink formulations, which contain hydroxyphenylbenzotriazole light absorbers produced as water-soluble sulfonate salts. The use of ink formulations containing water-soluble porphines as light absorbers is described in U.S. Pat. No. 5,891,229.
Another approach in the attempt to improve ink jet fade resistance has been to add stabilizers to ink jet coating formulations. U.S. Pat. No. 4,926,190 describes the addition of substituted hydroxyphenylbenzotriazole derivatives to a coating mixture. The use of water-soluble ultraviolet absorbers in a coating formulation is described in U.S. Pat. No. 5,096,781.
The use of water-soluble light stabilizers in ink jet receptive coatings has proven to be somewhat inefficient in that the stabilizers tend to migrate into the fibers of coated fiber-containing substrates. This same migration problem is faced by ink formulations that contain stabilizers as formulation additives; and once the ink is separated from its aqueous polymeric vehicle, the dye is open to interaction with ambient conditions. However, if the stabilizers were not water-soluble, their oleophilic nature would not allow appreciable concentrations of the stabilizers in aqueous based coating systems when employed as formulation additives.
Another problem often experienced with the use of light stabilizers as formulation additives is the tendency of the stabilizers to be extruded out of the substrate (a condition known as xe2x80x9cbloomingxe2x80x9d). Such blooming can cause a lost in effectiveness as well as dust formation problems.
Therefore, an object of this invention is to solve these major problems by disclosing cationic core-shell particles which exhibit properties that make them suitable for formulating ink jet receptive coatings.
Another object of this invention is to disclose cationic core-shell particles.
A further object of this invention is to disclose core-shell particle latexes.
Another object of this invention is to disclose efficient, economical ink jet receptive coatings that are resistant to blooming.
The objects of this invention are met via the production of cationic core-shell particles having a polymeric core component and a polymeric shell component disposed generally about said core, wherein said shell contains a stabilizer that is covalently bonded to the shell. As used herein the term xe2x80x9cstabilizerxe2x80x9d means a compound which contains in its molecular chain sites possessing ultraviolet absorbing activity, free radical scavenging activity, antioxidant activity, and/or peroxide decomposing activity.
Due to the core-shell morphology of the particle, only the shell component contains stabilizer (which is covalently bound to the shell polymer). This is an improvement over prior technologies in that the present invention permits placement of the stabilizer where the dye is actually adsorbed into the ink jet receptive coating. Moreover, the core-shell morphology allows one to use smaller quantities of the stabilizer while effecting a greater surface concentration.
The covalent bonding of the stabilizer to the shell component avoids the migration problems often associated with the use of water-soluble light stabilizers as formulation additives to inks or ink jet receptive coatings. Additionally, the binding of the stabilizer into the polymer backbone of the shell component prevents blooming.
The cationic core-shell particles suitable for use in formulating ink jet receptive coatings comprise:
(A) a polymeric core component, said core component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 80.0% to about 99.5% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof;
(2) about 0.5% to about 20.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof; and
(3) a catalytic amount of polymerization initiator; and
(B) a polymeric shell component disposed generally about said core component, said shell component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 70.0% to about 99.5.0% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof;
(2) up to about 30.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof;
(3) about 0.5% to about 30.0% by total weight of the mixture of stabilizer selected from the group consisting of ultraviolet absorbers which contain at least one ethylenically unsaturated group, radical scavengers which contain at least one ethylenically unsaturated group, antioxidants which contain at least one ethylenically unsaturated group, peroxide decomposers which contain at least one ethylenically unsaturated group, and combinations thereof; and
(4) a catalytic amount of polymerization initiator; and wherein said stabilizer is covalently bound to said shell component.
Preferred cationic core-shell particles comprise:
(A) a polymeric core component, said core component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 85.0% to about 95.0% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof;
(2) about 5.0% to about 15.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof; and
(3) a catalytic amount of polymerization initiator; and
(B) a polymeric shell component disposed generally about said core component, said shell component comprising the free radical polymerization reaction product of a mixture comprising:
(1) about 80.0% to about 95.0% by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof;
(2) up to about 15.0% by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof;
(3) about 5.0% to about 20.0% by total weight of the mixture of stabilizer selected from the group consisting of ultraviolet absorbers which contain at least one ethylenically unsaturated group, radical scavengers which contain at least one ethylenically unsaturated group, antioxidants which contain at least one ethylenically unsaturated group, peroxide decomposers which contain at least one ethylenically unsaturated group, and combinations thereof; and
(4) a catalytic amount of polymerization initiator; and wherein said stabilizer is covalently bound to said shell component.
The polymeric core component comprises from about 60% to about 90% of the total weight of the core-shell particle. It is preferred that the core component constitute from about 70% to about 88% of the total weight of the particle.
The polymeric core component comprises the free radical polymerization reaction product of a mixture comprising:
(1) about 80.0% to about 99.5% preferably from about 85.0% to about 95.0%) by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof;
(2) about 0.5% to about 20.0% (preferably from about 5.0% to about 15.0%) by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof; and
(3) a catalytic amount of polymerization initiator.
It is preferred that the ethylenically unsaturated monomer containing at least one quaternary ammonium group employed in the production of the polymeric core component be a salt selected from the group consisting of vinylbenzyltrimethylammonium salts, acryloyloxyethyltrimethylammonium salts, acryloyloxyethyldiethylmethylammonium salts, methacryloyloxyethyltrimethylammonium salts, methacryloyloxyethylbenzyldimethylammonium salts, acryloyloxyethylbenzyldimethylammonium salts, 2-Hydroxy-3-methacryloyloxypropyltrimethylammonium salts, 2-Hydroxy-3-acryloyloxypropyltrimethylammonium salts, methacrylamidopropyltrimethylammonium salts, and combinations thereof; wherein said salt contains at least one counter anion selected from the group consisting of halides, sulfates, alkylsulfates, arylsulfates, and combinations thereof. It is further preferred that the counter anion be a member selected from the group consisting of chloride, bromide, methosulfate, sulfate, and combinations thereof.
The polymeric shell component comprises from about 10% to about 40% of the total weight of the core-shell particle. It is preferred that the shell component constitute from about 12% to about 30% of the total weight of the particle.
The polymeric shell component comprises the free radical polymerization reaction product of a mixture comprising:
(1) about 70.0% to about 99.5% (preferably from about 80.0% to about 95.0%) by total weight of the mixture of a member selected from the group consisting of acrylic esters of alcohols containing from 1 to 22 carbon atoms, methacrylic esters of alcohols containing from 1 to 22 carbon atoms, styrene, substituted styrenes, acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl ethers, vinyl esters, N-vinyl amides, acrylamides, methacrylamides, and combinations thereof;
(2) up about 30.0% (preferably up to about 15.0%) by total weight of the mixture of a member selected from the group consisting of ethylenically unsaturated monomers containing at least one quaternary ammonium group and combinations thereof;
(3) about 0.5% to about 30.0% (preferably from about 5.0% to about 15.0%, and more preferably from about 5.0% to about 12.0%) by total weight of the mixture of stabilizer selected from the group consisting of ultraviolet absorbers which contain at least one ethylenically unsaturated group, radical scavengers which contain at least one ethylenically unsaturated group, antioxidants which contain at least one ethylenically unsaturated group, peroxide decomposers which contain at least one ethylenically unsaturated group, and combinations thereof; and
(4) a catalytic amount of polymerization initiator.
The dyes that are commonly employed in aqueous ink jet inks are anionic, containing sulfonic acid groups. The cationic nature of the core-shell particle serves to fix such anionic dyes. Where desired, the core-shell particle""s cationic nature may be increased by incorporating ethylenically unsaturated monomer containing at least one quaternary ammonium group in the production of the polymeric shell component. Where employed, it is preferred that said ethylenically unsaturated monomer be a salt selected from the group consisting of vinylbenzyltrimethylammonium salts, acryloyloxyethyltrimethylammonium salts, acryloyloxyethyldiethylmethylammonium salts, methacryloyloxyethyltrimethylammonium salts, methacryloyloxyethylbenzyldimethylammonium salts, acryloyloxyethylbenzyldimethylammonium salts, 2-Hydroxy-3-methacryloyloxypropyltrimethylammonium salts, 2-Hydroxy-3-acryloyloxypropyltrimethylammonium salts, methacrylamidopropyltrimethylammonium salts, and combinations thereof; wherein said salt contains at least one counter anion selected from the group consisting of halides, sulfates, alkylsulfates, arylsulfates, and combinations thereof. It is further preferred that the counter anion be a member selected from the group consisting of chloride, bromide, methosulfate, sulfate, and combinations thereof.
The incorporation of a stabilizer in the free radical polymerization reaction results in the stabilizer being covalently bonded to the polymeric shell component. Any ultraviolet absorber, radical scavenger, antioxidant, or peroxide decomposer which contains at least one ethylenically unsaturated group (thereby being capable of covalent bonding to the polymeric shell component via free radical polymerization reaction) is suitable for use in the present invention. Commonly known methods of producing such compounds containing at least one ethylenically unsaturated group include acryloyation and reacting the compound to be modified with a reactant that contains at least one acryloyl group (e.g., glycidyl (meth)acrylate or isocyanatoethyl (meth)acrylate). Where an ultraviolet absorber is employed as a stabilizer it is preferred that the absorber be a member selected from the group consisting of hydroxyphenylbenzotrazoles containing at least one ethylenically unsaturated group, hydroxyphenylbenzophenones containing at least one ethylenically unsaturated group, porphines which have been modified to contain at least one ethylenically unsaturated group, and combinations thereof. Where a radical scavenger is employed as a stabilizer it is preferred that the scavenger be a member selected from the group consisting of tetramethylpiperadine derivatives containing at least one ethylenically unsaturated group and combinations thereof. Where an antioxidant is employed as a stabilizer it is preferred that the antioxidant be a member selected from the group consisting of sterically-hindered phenols containing at least one ethylenically unsaturated group, diarylamines containing at least one ethylenically unsaturated group, and combinations thereof. Where a peroxide decomposer is employed as a stabilizer it is preferred that the decomposer be a member selected from the group consisting of triphenyl phosphites which have been modified to contain at least one ethylenically unsaturated group, mercaptans which have been modifed to contain at least one ethylenically unsaturated group, and combinations thereof. Suitable modified triphenyl phosphites and modified mecaptans (such as modified thiodipropionic acids, thiobenzimidazoles, bisaryldisuophides, and the like) may be produced by any method which results in the modified compound containing at least one ethylenically unsaturated group. For example, triphenyl phosphite can be prepared with a combination of styryl phenol and 2,4-di-tertiary butyl phenol. Likewise, thiodipropionic acid can be reacted with glycidyl methacrylate to produce the modified compound. The polymeric shell component does not not swell upon pH adjustment.
Where desired, the core-shell particle may comprise a plurality of shell components, each disposed about the core component.
A catalytic amount of polymerization initiator is used in the free radical polymerization reactions. The amount of initiator employed commonly comprises from about 0.1% to about 3.0% (preferably from about 0.2% to about 2.0%) by weight of the total mixture used to produce the respective polymeric component. Traditional polymerization initiators (such as thermal initiators, redox initiators, and the like) are suitable for use in the free radical polymerization reaction. Examples of suitable thermal initiators include, but are not limited to, the following: hydrogen peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, benzoyl peroxide, benzoyl hydroperoxide, 2,4-dichlorobenzoyl peroxide, t-butyl peracetate, azobisisobutyronitrile, isopropyl peroxycarbonate, and combinations thereof. Examples of suitable redox initiators include, but are not limited to, the following: cumene hydroperoxide-sodium metabisulfite, cumene hydroperoxide-iron (II) sulfate, and combinations thereof. Preferred initiators include water-soluble azo compounds (such as V-50 or VA-086 manufactured by Wako Chemicals).
While any free radical polymerization reaction is suitable for use in the present invention, it is preferred to employ either an emulsion polymerization reaction or a suspension polymerization reaction. The use of an emulsion polymerization reaction is more preferred.
Latexes suitable for use as ink jet receptive coatings in the present invention include aqueous suspensions of cationic core-shell particles. It is preferred that such latexes have a solids content in the range of about 20.0% to about 60.0%, with the more preferred range being about 30.0% to about 45.0%.
The latexes of the present invention are excellent ink jet receptive coatings which impart superior fade resistances. Such ink jet receptive coatings can be employed to produce ink jet printable products via the process of coating a chosen substrate on at least one side with the ink jet receptive coating. Substrates which are suitable for use in producing such ink jet printable products include paper, paperboard, wood, plastic film, metal foil, textiles, and the like. Where desired, any of the pigments traditionally used in ink jet receptive coatings can be employed in the coating provided that the pigments are compatible with a cationic coating. Such pigments include, but are not limited to, the following: silica, alumina, plastic pigments, calcium carbonate, kaolin clay, and combinations thereof.